5mm Red LED
The lowest forward-voltage common LED — the standard first component in beginner circuit kits.
How this component works
An LED is a diode built from a semiconductor that emits photons when electrons cross its junction. Like any diode, it only conducts in one direction and has a forward voltage drop — but that drop depends on the LED's color, since color corresponds to the semiconductor's bandgap energy (red and infrared LEDs have the lowest forward voltage, blue and white the highest).
Because an LED's resistance drops sharply once it starts conducting, it must always be paired with a current-limiting resistor — connecting one directly across a supply voltage higher than its forward voltage will destroy it almost instantly.
CircuitForge lets you set the forward voltage directly, which is the one parameter that changes between LED colors in the simulation.
Common Use Cases
- Power/status indicator on a 5V or 9V circuit
- First LED-plus-resistor circuit for learning Ohm's Law
- Output indicator on a transistor or logic-gate switch
Frequently Asked Questions
What resistor should I pair with a red LED on 5V?
A 220Ω or 330Ω resistor keeps current around 15-20mA on a 5V supply — try it in the simulator and check the ammeter reading before committing to real hardware.
Why is red the lowest forward-voltage color?
Forward voltage tracks the semiconductor's bandgap energy, and bandgap energy tracks photon energy — red light has the lowest photon energy of the visible spectrum, so red LEDs need the least voltage to turn on.